The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
As is known, an aircraft engine nacelle allows conveying outside air toward the engine, of the turbojet engine type for example, and providing the ejection of air at high velocity so as to provide thrust.
In bypass turbojet engines, the air flow mixed by the fan is divided, downstream thereof, into a primary flow (also said “hot”) which enters inside the core of the turbojet engine in order to undergo several compressions and an expansion, and a secondary flow (also said “cold”), which circulates inside a substantially annular flow path, defined on the one hand by a fairing of the engine (fixed internal structure, also called “IFS”), and on the other hand by the thickness of the nacelle.
The cold air flow, coming out downstream of the nacelle via an output nozzle defined by the downstream edge of the nacelle, provides most of the thrust.
Moreover, as is known, the nacelle incorporates very frequently thrust reversal means, allowing directing a portion of the secondary air flow upstream of the nacelle during landing, thereby actively contributing to the braking of the aircraft.
These thrust reversal means are often of the cascade type, that is to say that they include a series of vanes arranged downstream of the fan casing, at the periphery of the flow path of cold flow. These vanes can be uncovered on request by a thrust reverser cowl slidingly mounted on the structure of the nacelle.
In addition to a thrust reversal function, a movable thrust reverser cowl belongs to the rear section of the nacelle and may have a portion forming an ejection nozzle.
The section of the ejection nozzle of the cowl can be adjusted depending on the different phases of flights, which may in particular include take-off, climb, cruise, descent and landing in order to always keep a desired nozzle section depending on the turbojet engine speed. The nozzle will then be called variable section nozzle.
Such a variable section nozzle is associated with an actuating system allowing this section variation.
There are several solutions to make a variable section nozzle.
In particular, there is known a nacelle described and represented in the document FR-2622929, which is equipped with a movable thrust reverser cowl which has an upstream section intended to cover the cascade vanes, and a downstream section forming a variable section nozzle.
According to this document, the downstream section of the cowl has a generally annular shape, the downstream section being slidingly mounted axially on the upstream section to clear a leakage passage between the downstream section and the upstream section of the cowl.
This leakage passage allows a portion of the air flow flowing in the secondary flow path to be ejected, which amounts to expanding the section of the nozzle formed by the cowl.
Although this type of nacelle allows effectively varying the section of the nozzle, it has some disadvantages.
Indeed, the mechanical connection between the downstream movable annular portion and the upstream portion of the cowl constitutes a mechanical weakening of the nacelle.
In addition to weakening the thrust reverser cowl, this mechanical connection may also generate vibrations of the downstream annular portion of the cowl during the operation of the engine.